The basic operation and structure of a land mobile communication system is well known. Land mobile communication systems typically comprise one or more communication units (e.g., vehicle-mounted or portable communication units in a land mobile system and communication unit/telephones in a cellular system) and one or more repeaters that transceive information via radio frequency (RF) communication resources. These communication resources may be narrow band frequency modulated channels, time division multiplex slots, frequency pairs, and so forth. Land mobile communication systems may be organized as trunked communication systems, where a plurality of communication resources is allocated amongst a group of users by assigning the repeaters on a communication-by-communication basis within an RF coverage area. Typically, one or more zone controllers, or other trunked communications controllers, providing similar functionality, controls communications throughout the system by transceiving control messages with communications devices, such as site controllers or intelligent repeaters, throughout the system.
In many of today's trunked communication systems, a zone controller needs to convey information to the communication units. Communications from a zone controller are transferred to one or more communications devices at each site and then transmitted over a control channel provided between the site and the communication units. Because these messages arrive at the site asynchronously, but are transmitted over the control channel, synchronously, the messages are placed in a queue for transmission on the control channel, and messages are selected for transmission from the queue on a first in, first out basis (FIFO). Because the messages all flow through the queue in a sequential manner, messages are not selected for transmission on any other basis other than on a FIFO basis. Messages may be delayed due to heavy loading, and some messages may actually be transmitted long after their usefulness has expired (stale messages). When stale messages are transmitted, bandwidth is wasted and transmission of useful information is further delayed. Some systems will discard messages when the queue becomes long, thereby compromising message reliability, as the discarded messages tend to be message repeats that are established to improve reliability. In addition, many standards, such as IS-102 (APCO-25), may limit any changes to the air interface that could increase control channel capacity.
Accordingly, there is a need for a method of transmitting messages that provides for control channel sequencing without compromising message reliability, wasting bandwidth, or unnecessarily delaying transmission of messages.